The present invention relates to an electric high-voltage circuit breaker, the movable contacts of which, arranged in interrupter units supported by support insulators, are actuated via a switching rod of insulating material and a reversing gear at ground potential, by a hydraulic drive, the piston rod of which, going through a seal, is brought out of the hydraulic cylinder and is connected via a fork head provided with a guiding ring on its side facing the piston rod and guided in a protective tube, to the reversing gear, and in which the hydraulic cylinder is located between two housings for parts of the drive, in the interior spaces of which a heater and connections for ventilating and exhausting are arranged.
Such a design of an electric high-voltage circuit breaker is generally customary and is known particularly from DE-AS 29 13 379. During the switching of such an electric high-voltage circuit breaker mounted in the open, the piston rod coming from the hydraulic cylinder moves back and forth. Thereby, the seal between the hydraulic cylinder and the piston rod is heavily stressed, since the danger exists that impurities are deposited on the extended part of the piston rod such as dust or moisture, so that also corrosion phenomena can occur. For this reason, a protective tube is provided, the length of which is made so that the fork head connected to the piston rod remains also in extended condition (ON-position of the breaker) with its side facing the piston rod and provided with a guiding ring in the protective tube.